- handlerData: Data passed to the initiating call.
- furtherAuth: Pointer to a FurtherAuth.
- passwordChange: Pointer to a PasswordChange.
When doing FurtherAuth: Return false to stop user authentication and disconnect.
When doing PasswordChange: Return false to abort password change and continue with user authentication (most likely raising FurtherAuth in the process).
FurtherAuth and PasswordChange are always exclusive - one will be NULL.
FurtherAuth: Invoked if the server needs additional data, for instance a password or a keypair, to authenticate the user.
PasswordChange: If a password has expired, the server will usually request a new password from the user.